The present invention relates to processing polychloroprene contact adhesives and processes for making the same to improve their sprayability. The present invention more particularly relates to making high solids/high acetone containing polychloroprene contact adhesives that can be atomized for spraying.
It has been generally known in the field of high solids contact adhesives that in order to comply with VOC regulations, contact adhesives would have to be either chlorinated solvent products or waterborne products.
The early contact adhesives which complied fully with the VOC regulations were chlorinated solvent based. However, the Montreal Protocol banned the use of methyl chloroform based on its potential as an upper atmosphere ozone formation retardant. This left only methylene chloride as a possible solvent for contact adhesives.
In 1997, the Hazardous Air Pollutants regulation, 40 C.F.R. Part 63 (the Wood Furniture NESHAP) made methylene chloride a hazardous air pollutant. Furthermore, on Jan. 10, 1997, the U.S. Office of Occupational Safety and Health (OSHA) issued a standard (29 C.F.R. Parts 1910, 1915 and 1926) which lowered the limit on worker exposure to methylene chloride. Based on these regulations, it appeared that the only alternative to these chemicals were waterborne contact adhesives.
In 1997, a third alternative became possible because of two factors. The first was the delisting of acetone as a Volatile Organic Compound (VOC) by the EPA. The second was the development of technology which enabled aerosolization of polychloroprene phenolic contact adhesives. A polychloroprene contact adhesive when coated on two materials, adheres to itself upon contact, after drying. Polychloroprene contact adhesives have been formulated in both solvent and waterborne systems. The materials upon which polychloroprene can be used include wood, plastic laminates, paper, glass, carbon filter, concrete, ceramics and metals such as iron, steel and aluminum.
There is a need for a polychloroprene contact adhesive that can be sprayed from an aerosol container in a uniform spray pattern. There is a further need for a polychloroprene contact adhesive that can be sprayed from a standard pressurized container with pressure regulator and/or valves and nozzles that are commercially available, for example, the Binks Spraypot.
It would therefore be useful to develop a polychloroprene contact adhesive which was made from high solids which makes it possible to accomplish more work per unit of adhesive. This also allows for less solvent evaporation into the air while completing the same amount of work. It would also be useful to develop a polychloroprene contact adhesive which surpasses the Wood Furniture NESHAP mandated Hazardous Air Pollutants (HAP) level of one pound HAP per pound of solids. The invention allows the creation of contact adhesives which contain HAP levels of less than 0.2 and possibly as low as zero HAP.
According to the present invention, a method of making a contact adhesive includes the steps of mixing a solvent with a rubber blend and/or resin for making a contact adhesive and then processing the solvent/rubber/resin blend until a desired lowered viscosity is reached while obtaining a solids content of not less than 30 weight percent. Also described is a high solid/high acetone contact adhesive made of a mixture of polychloroprene or a polychloroprene derivative and acetone.
The present invention provides a method of making a contact adhesive and the contact adhesive per se. The method most generally includes the steps of first mixing a solvent with a rubber blend and resin to form a solvent/rubber/resin blend of the type to be used as a contact adhesive. The solvent/rubber/resin blend is processed until a desired lowering of the ASTM D 1084 Saybolt viscosity is reached, while achieving a solids content of greater than 30 weight percent. This process can be accomplished in multiple steps to raise the solids content while continuing to lower the viscosity to a desirable level well suited for spraying uses. High solids products make sense in an era of accelerating solvent prices and VOC regulations. With very high solids products it is possible to deliver more bonded area per gallon, thus less solvents evaporate into the air when performing a given amount of work. Since less solvents evaporate into the air per unit of adhesive sprayed the HAP and VOC levels are lowered. In addition, the increased solids content allows users to achieve a desired adhesion with less spray. Users, therefore, do not need to spray as long and thus again fewer pollutants are released.
In fact, The Wood Furniture NESHAP mandated a HAP level for existing regulated sources of 1 pound of HAP per pound of solids and new sources to 0.2 pounds of HAP per pound of solids. The contact adhesive of the present invention is capable of attaining HAP levels of 0.2 or less and VOC levels of less than 400 g/L.
More specifically, the solvent/rubber/resin blend can be made in a kettle type process well known in the art. Solvents of the type used in the present invention can be selected from the group including aromatics, ketones, aliphatics, alcohols and esters. The concentration of solvent can range from 35 to 70%, by weight.
Resins used with the present invention can be selected from the group including modified resins, polyterpene resins, phenolic resins, phenolic modified terpene resins, and aliphatic petroleum hydrocarbon resins. Preferably, phenolic resins are used. Broadly, the resins can range from 4 to 30 weight percent. More preferably, the resins range from 6 to 25 weight percent. The weight percent of resin relates linearly to the weight percent of solids. For example, the weight percent of resin in the adhesive is 14 when the solids level is 36% and 25 when the solids level is 65%.
The rubbers used are well known in the art. Preferably, the rubber used is a blend of polychloroprene synthetic rubbers in a broad concentration ranging from 8 to 40 weight percent. More preferably, the rubber concentration ranges from 10 to 36 weight percent. The preferred rubber concentration is 20 weight percent.
The total solids concentration is greater than 30 weight percent. Surprisingly, solids levels have ranged from 30% to 65%, previously unheard of levels. Also, unheard of levels of acetone have been able to be used in the same mixture. Acetone levels have exceeded 60% of solvent blend by volume, thus providing high solids and high acetone adhesives having Volatile Organic Compounds (VOC""s) below the 250 g/L mandated by SCAQMD and even below the 200 g/L mandated by other California districts.
The processing step discussed above is most preferably accomplished by shearing the solvent/rubber/resin blend to achieve the desired viscosity. The shearing process is discussed in detail in U.S. Pat. No. 5,733,961 to Purvis II, et al., issued Mar. 31, 1998. The Purvis II, et al ""961 patent is incorporated herein by reference. Generally, the processing step includes shearing in a Microfluidizer(copyright) processor utilizing an electrically driven, dual plunger or piston, hydraulic intensifier pump to pressurize the fuild product.
During the operation the solvent is mixed with rubber and/or resin in a kettle type process to form a blend and then introduced into the Microfluidizer(copyright) wherein the high pressure plungers/pistons in the pump shift back and forth forcing the blend out of one end of the pump, while drawing the blend into the other end. The pump""s action forces the blend stream into the restricted orifice of the interaction chamber. The chamber""s microchannels are geometrically fixed and the pathway is comparable in size to the cross section of a human hair. Once inside, the blend stream becomes highly pressurized and propels forward at speeds of up to hundreds of meters per second. It separates in two, changes direction and collides with itself into a single stream. There is incredible amount of energy being dissipated in an extremely short period of time creating shear, impact and cavitation. End particles and droplets will be dramatically reduced in size. Thereafter, if desired, more solvent, rubber and/or resin is added to the blend in a kettle type process and the new blend is introduced into the Microfluidizer(copyright) for further processing.
The product that enters the processing zone encounters no moving parts. There is nothing to fluctuate as the pressure accelerates or decelerates and thus cause inconsistencies from batch to batch. Additionally there are no crevices or obstacles to collect particles and complicate cleaning. Results are consistent and easily reproducible.
The particular type of polychloroprene which will be utilized depends upon the properties (e.g. flammability, oil resistance, toughness, extensibility, crystallization rate, resistance to crystallization, etc.) which are required in the contemplated use.
Commercially available tackifiers for polychloroprene contact adhesives include natural and modified resins, polyterpene resins, phenolic resins, phenolic modified terpene resins, and aliphatic petroleum hydrocarbon resins.
Metallic oxide, such as magnesium and zinc oxide, serves as acid acceptors by neutralizing the hydrochloric acid which is released upon the aging of polychloroprene, thereby minimize the deterioration of materials that come into contact with the polychloroprene contact adhesives. They serve, furthermore, as curing agents for the polychloroprene, thereby increasing the tensile strength of the resulting adhesive bonds, and also aid in the room temperature crosslinking.
The antioxidant prevents oxidation and discoloration. The following antioxidants have been disclosed as suitable for use in formulating polychloroprene contact adhesives: phenyl-alpha-naphthylamine, phenyl-beta-napthylamine, phenyl-beta-napthalene, and 2,2xe2x80x2-methylene-bis (4-methyl-6-tertiary butyl-phenol).
The desired lowering of the VOC is reached at a value of below 400 grams per liter. Preferably, the desired VOC is within the range of 200 to 400 grams per liter and in a preferred embodiment is 390 grams per liter. In accordance with the present invention, the processing step, especially using the shearing process of the present invention, can cause drops in viscosity of ten to over 70%. Thus, viscosity ranges allow for spraying via a pressurized canister or pressurized spraypot, as well as, aerosol spraying through small volume applications.
Examples of such aerosol spray mechanisms are disclosed in U.S. Pat. Nos. 4,401,272 and 5,444,112. The ""272 patent discloses an aerosol spray nozzle structure which enables a formulation of aerosol adhesives based on soluble polychloroprene. However, the ""272 patent discloses that the spray head permits an aerosol solids level as high as 11.1%. Utilizing the present invention, such aerosol spray nozzles can spray solids at concentrations well above 11.1%.
Depending on the amount of adhesive being used for a particular type of application, the adhesive prepared as described above may be packaged in unpressurized bulk containers like 55 gallon drums or 5 gallon pails. Bulk container adhesives can be applied with pressurized spray pot systems.
The present invention further provides a contact adhesive made by the above-described method. Most generally, the contact adhesive is a solvent/rubber/resin blend having a ASTM D 1084 Saybolt viscosity capable of atomizing and a solids content of greater than 30 weight percent.